1. Field of the Invention
The present invention relates in general to a method for weld inspection and defect analysis, and more specifically to an automated method for non-destructive inspection and evaluation of a butt weld through the use of ultrasonic waves.
2. Description of the Related Art
A variety of industries use sheet metal which is produced typically at a factory from ingots processed by a rolling mill. Ingots are heated and rolled by the mill into a long flat sheet which is then wound into a coil at the end of the mill. Thereafter, the coil is removed from the mill and shipped to other sections of the factory where further treatment processes are performed. To make these other processes have fewer interruptions, the coil is unrolled and joined at one of its ends to the end of another coil by an electric resistance weld which generally is in the form of a butt weld. Any number of coils may be welded together in such fashion, depending upon the desired length of process run. Weld defects, however, can cause a weld to break during a process run, resulting in costly equipment damage, production delays and wasted material.
In order to identify and remedy weld defects before they can cause breaks and consequential production problems, non-destructive testing of the welds can be performed. An inspection device is known that uses ultrasonic waves to non-destructively test the welds shortly after they have been made. The device employs Electromagnetic Acoustic Transducers (EMAT) which are arranged to transmit and receive what are known to be SH shear waves. The SH shear waves are launched by a transmitter meander coil EMAT, and the waves travel through the sheet metal to the weld where they are reflected back through the sheet metal and are received by a separate receiver meander coil EMAT located near the transmitter. During this non-destructive test, the reflected wave produces an electrical signal in the receiver coil, which is monitored while both the transmitter coil and the receiver coil are scanned close to the surface of the sheet metal, parallel to the weld line, and over the full width of the sheet metal. During the scanning, the amplitude of the signal produced in the receiver coil is measured and used to indicate the quality of the weld.
The known device is retrofitted into a flash butt welding machine on a production line, and a motorized transport apparatus into which the transmitter and receiver coils are mounted is used to carry out each weld scan. Unlike the method of the present invention, operation of the known device requires full-time control by a human operator, who, through the manipulation of push buttons, moves and positions the transport apparatus with the transmitter and receiver coils onto and across the sheet metal surface subsequent to the making of each weld by the welding machine. Results of the test, i.e., the measured amplitude of the receiver coil signal, are recorded on a device such as a strip chart recorder and are monitored and interpreted by the human operator.
References of interest are U.S. Pat. No. 4,295,214 to Thompson, which discloses an Ultrasonic Shear Wave Transducer, and D. T. MacLauchlan, G. A. Alers and J. J. Jackson, "Detection and Measurement of Defects in Butt Welds", Review Of Progress In Quantitative Nondestructive Evaluation, 1989, p. 1039.